The invention relates to a method to determine the lubricant filling degree of a fluid bearing in which the bearing gap of the fluid bearing is illuminated and the luminous reflectance is analyzed.
Hydrodynamic bearings, also called fluid bearings, are used, for example, for the rotary bearing of high-precision spindle motors as employed in hard disk drives. Compared to ball bearings, hydrodynamic bearings display high running precision and silent running combined with much higher shock resistance (robustness). They operate almost noiselessly and practically without wear and tear since at nominal speed there is no direct physical contact involving dry friction between the bearing parts that rotate in relation to each other. Between the shaft and the shaft receptacle (bearing sleeve), there is a thin layer of lubricant, such as a lubricant oil.
A method to determine the lubricant filling degree of a fluid bearing is known, for example, from JP 2001-090733 A. Using such a method, it is possible to check whether the desired filling level has been achieved during the manufacture of the bearing, that is while it is being filled or also after it has been filled.